588 Wisconsin Academy of Sciences, Arts, and Letters. 
Similar experiments were tried, using the blue and red 
glasses. Only at two centimeters from the red did a majority 
of the sporanges reach the red glass. At ten centimeters, none 
were fired toward the red. Table XIX gives the data for these 
experiments. As in the case of the red and white lights, twelve 
times as many sporanges all told were fired toward the blue as 
toward the red light (Figure 19). 
As in the preceding cases, the accuracy of aim toward either 
light appears to be unaffected by the presence of the other. 
Table XIX .—Culture at distances indicated. Openings 2 cm. in diameter. 
Blue aud red lights at opposite ends of the box. 
Distance from red. 
2 cm. 
4 cm, 
8 cm. 
10 cm. 
Number on red... 
68 
10 
1 
0 
Per cent on red. 
78.1 
11.5 
4 
0 
Distance from blue. 
36 cm. 
34 cm. 
30 cm, 
28 cm. 
Number on blue. 
19 
77 
27 
41 
Per cent on blue. 
21.8 
88.5 
96+ 
100 
GENERAL DISCUSSION 
The wide upper part of the top-shaped vesicular bulb of 
Pilobolus is broader than the sporange which caps it; conse¬ 
quently, when the sporangiophore is pointing directly toward 
a small source of light, only the sporange and a narrow rim 
around the upper end of the vesicular bulb are exposed to 
direct illumination. The slender stalk below the bulb under 
such circumstances is shaded. 
Steyer (21) has obtained evidence that in Piny corny ces the 
sensitive and motor zones in the sporangiophore coincide and 
are located just below the sporange. In Pilobolus, after spo¬ 
range aud vesicular bulb are formed, the motor zone is in the 
upper end of the sporangiophore, just below the vesicular bulb. 
If, as in Phycomyces, the motor is also the sensitive region, 
the fiual adjustment in the process of aiming, that is, after 
the sporangiophore has come to point almost directly toward 
the light, is not made under the influence of direct illumination; 
for such light as reaches this portion of the stalk must have been 
